Update: We made it back up close in July of 2022.
We went back to try and get a better view of what I discovered were old railroad machine shops in Oelwein, which I had viewed back in the fall of 2018 (seventh photo down). Unfortunately, due to the height of the undergrowth, the buildings were largely obscured. But they are massive, and dominate the center of town. I strongly suspect the buildings are the one located below in the Sanborn map from 1914; they are the building on the far left that form an inverted letter “L.” As can be seen, they were once part of a massive railcar manufacturing operation.